1. Field of the Invention
This invention relates to footwear and a method of manufacture thereof.
2. Background of the Invention
In the manufacture of footwear, as set forth in U.S. Pat. No. 3,758,903, it is known to provide a loading station of a sole attaching device wherein the upper is placed on a last and secured in its position thereafter by a side frame forming part of the sole mold cavity. After locking the side frame against the last, the unit is moved to a molding station to close a sole cavity where, preferably by injection molding, a sole is formed and bonded to the bottom margin of the upper. The sealing of the sole cavity against the upper is obtained by a lip of the side frame which has to be relatively heavy to withstand the pressure of the sole material.
Also, in the manufacture of stitch-down shoes, it is known to use a lip plate separated from the sole cavity member wherein the lip plate is provided with a blanking knife edge. The lip plate serves as an anvil plate and is, therefore, subjected to heavy pressure which is required to cut through both the upper material and the stitch-down midsole.
It is still further known from U.S. Pat. No. 3,965,517 to provide a prewelted upper which is lasted without structural insole or midsole on the last of a sole molding device having a divided lip plate. The lip plate is used to locate and position the welt in the desired final position while the shoe bottom is freely accessible for visual inspection and before the unit of last, upper, lip plate and lip plate positioning means are brought into juxtaposition with the sole molding cavity parts comprising a side wall and a bottom wall member. In this position with an enclosed cavity, the welt is clamped between the lip plate and the rim of the molding cavity to assure both a reliable sealing of the molding cavity and also a spacing in the form of an air gap between the lip plate and the cavity rim. This spacing prevents essential heat transfer from the cavity member to the lip plate. Even if the cavity member, such as the side frame, is maintained at high heat for rapid vulcanization of the sole elastomer (rubber), the lip plate remains at a much lower temperature, thus enabling easy handling of the lip plate during loading, lasting and unloading of the mold last.
In the use of sole attaching devices in which the upper, mounted on a last, is moved from a loading to a sole attaching station, the invention provides for the use of a light lip plate not only to facilitate the handling in placing and locking the lip plate against the upper, but also the use of the lip plate so that heavy pressure against the lip plate is avoided. This prevents distortions of the lip plate and the danger of damage to the upper and/or faulty sealing. At the same time, it is possible to refrigerate the sole cavity member, comprising both side and bottom walls, before moving the cavity member to the molding position of an injection molding sole attaching device.
It is also known to place a pre-vulcanized rubber tread sole in the mold cavity and inject polyurethane into the mold to make a bond to both the tread sole and the upper.
Relative to rubber as a soling material, prior art use of polyurethane has displayed poor oil resistance, poor crack resistance, poor skid resistance, poor abrasion resistance, particularly when expanded significantly, and poor flame resistance.